Gas and temp gauge gremlin

Hi everyone, its been a while. Has anyone had this one yet? Start Jeep and gas and temp gauge work like they are supposed too. About half the time now, start Jeep and both gauges just peg as soon as I turn the key to on. I don't know why it happens. I thought maybe the gas gauge sending wire was shorting out, but would that cause the temp gauge to peg? Any help??

 

Bad ground????

 

there is a set of contact points mounted on a bi-metal strip inside the gas guage, this strip is wound with a piece of small wire. when 12 volts is applied to the wire it heats up and makes the bi-metal strip bend and breaks the contacts, breaking the current path. as the strip then cools it bends back and the points make contact again. this happens repeatedly and very quickly and acts as a voltage regulator to give you roughly 5 volts to run both guages on (really it fluctuates between 0 and 12 to give you an average of 5 volts). if those points stick, full 12v system voltage will go through to both guages. eventually this will burn out the guages.

Hey, you asked

 

So how does one fix this gauge gremlin problem? My "new" 73CJ5(finally got around to getting it up and running) is having the exact problem. I'd rather keep it all original and not replace the original gauges if I don't have to do so.
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I would get an external gauge regulator and try it. Your FLAPS will carry the.. Don't forget the mounting tab has to bolt to a ground return.

 

One of the things about what $ sink describes is if you loose ground to the meter housing then it stops the regulator from heating allowing full current to pass through gauge pinning the meter.

You have to check the grounds to the case to be sure it's good. Many intermittent problems extend from a poor ground.

Here are a couple of quick test you can make.
http://home.roadrunner.com/~john.strenk/Gauge web page/CJSpeedometerGaugeQuickTest.htm

For those who want to know how they work. (Give a man a fish and that kind of stuff:
http://home.roadrunner.com/~john.strenk/Gauge web page/basic_troubleshooting_for_cj_gau.htm

If you just need some quick info on gauges:
http://civilianjeep.info/Strenk/Gauge web page/QuickFacts.htm

 

John-- As you and $ sink both elude to is the contact points on the bi-metal strip are in the locked closed position and passing full 12v to the gauges. I agree that this is what is happening so that is why I say to put an external regulator in the circuit which will then give the gauges the required average 5v necessary for proper operation. I think some early Mopar and also Fords used this system.

Walt

 

I will check the grounds. The speedo is shot too and makes a HORRIBLE and LOUD whining noise when rolling along. Maybe i will have to replace it all. Any ideas for that speedo fix? Maybe put in a working unit from another housing? Thanks.

 

Look at the back of the speedo where the cables srews into.
There is a little hole that needs to be oiled regularly.
It can also be a speedo cable vibrating due to lack of lubrication.

My speedo packed up that way.

Hope this helps.

 

Mine dose the same thing. I replaced the sending unit and gas gauge and fixed it. Then I replaced the speedometer and the new guages with it would not function, so I put the old guages in the new speedometer. It has never been right since. They ground to the other indicator lights in the speedometer - if you don't have these lights working it will not work. Mine will work some days if I reach under the dash and wiggle the gas guage wires. Most of the time it reads full regardless. I just fill it up evertime I pass a station.

 

The speedo's are easy to rebuild if you need to. There are a couple threads here where it was done. I can walk you through it if need be.

The sound might be from the speedo cable instead of the speedometer.

 

bad ground , fyi there is no ground wire back to the cluster, ground is thru frame, and water, time corrosion are your enemy